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| Turbines block one another's wind more than was originally thought |
DANISH wind energy titan Ørsted is having to rethink its science - and financial projections - after discovering that windfarms are not as energy-efficient as had been hoped.
The problem is that individual turbines have the effect of 'blocking' wind from another.
On a large scale, one windfarm is likely to reduce the wind on an adjacent development - perhaps one operated by a competitor.
Ørsted is important to Grimsby's economy because the town is Mission Control for its offshore projects in the southern North Sea.
The pioneering company's chief executive, Henrik Poulsen, sought to explain the 'blockage' factor is a presentation to analysts.
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| Henrik Poulsen - "it's complicated" |
Said he: "Forecasting offshore wind is inherently a complex task - you need to forecast the wind speed, its direction, how it flows, how strong it is at each turbine position.
"You also have to consider how it interacts with the turbine, how the turbines impact each other, how the wind at each position translates into electricity production and how often and when the turbines will be productive. The list goes on."
He continued: "Given the high number of variables and the use of advanced analytical models crunching millions of data points, such an exercise comes with a fair amount of uncertainty.
"We have concluded that our current production forecasts underestimate the blockage and wake effects across our asset portfolio.
"Blockage arises from the wind slowing down as it approaches an object, in this case our wind turbines.
"There is an individual blockage effect for every wind turbine position as well as a global effect for the whole wind farm which is larger than the sum of all of the individual effects.
"When the wind hits the front row of a wind farm, it will slow down as it approaches the front wall, so to speak.
"Our new wind simulation models suggest that we historically have underestimated these blockage effects.
"This finding is also supported by a recent report on blockage from industry consultants DNV GL which indicates that this effect is more broadly underestimated."
Mr went on: "The second effect is the wake within wind farms and between neighbouring wind farms.
"This effect where the turbines shield and impact each other has been subject to extensive modelling by the industry for many years and it is still a highly complex dynamic to model.
"We have now introduced a more advanced model for estimation of wake effects within a wind farm.
"It leverages data from our entire operational portfolio and benchmarks the predictions against production data from our scatter systems. The results point to a higher negative effect on production than earlier models predicted.
"With respect to wake effects between neighbouring wind farms, we are also here in the process of developing a new model capable of more accurately predicting wake effects over longer distances.
"We have, among other things, leveraged a first of its kind advanced radar system collecting three-dimensional data on the wind flow.
"This system has been used at the Westernmost Rough wind farm in the UK where it has given us a lot of new insight into the wind flows. We will also deploy it in Taiwan.
"The new model, albeit still being refined, suggests a slower wind speed recovery and therefore higher wake effects.
"At the same time, we have now factored in a more extensive offshore wind build-out in the different regions which will increase the wake effect from neighbouring wind farms.
"As the global offshore wind build-out accelerates, the whole industry will see higher wake effects from neighbouring wind farms.
"We have over the years benchmarked our internal production estimates against third-party views from industry experts and other developers.
"In comparison, most production estimates from third parties have been trending towards a more positive view than ours. Therefore, we do believe that underestimation of blockage and wake effects likely is an industry-wide issue.
"While the production deviation we have discovered is negative, I am firmly convinced that Ørsted’s unparalleled access to production data and our advanced analytics capabilities will help drive our competitive advantage.
"Getting smarter and gaining a more granular insight into our production dynamics is in itself a good thing, and it goes without saying that we will seek to leverage the recent findings to enhance the design of future wind farms.
"And while not immaterial, the forecast adjustment is not something that changes the competitiveness of offshore wind nor does it change Ørsted's ability to drive profitable growth.
"We remain very confident about both."
Asked to comment on the impact of neighbouring windfarms on one another, Mr Poulsen replied: "I cannot give you a very specific sort of threshold for when you start seeing these wake effects from a neighbouring wind farm, but you would probably be surprised how far out it actually has an effect.
"Let me put it this way, when you get sort of within 25 km it actually starts to have an impact.
"We can detect an impact further out, even beyond 25 km, but then it begins to be a very marginal and small, almost negligible impact but as you move within that 25 km boundary and down to sort 10-15-20 km, it begins to have a real impact. "
The company recently revealed that, as of early October, 2019, all 174 turbined had been installed at Hornsea 1 off the Yorkshire Coast.
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| 174 turbines now installed at Hornsea 1 - with many more to follow |
Ørsted also has extensive interests, onshore as well as offshore, elsewhere in Europe and in Taiwan and the USA.
* All photographs courtesy of Ørsted
** Available via Kindle as an e-book:
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